[1] Florida State Univ, Dept Phys, Tallahassee, FL 32306 USA
[2] Florida State Univ, Natl High Magnet Field Lab, Tallahassee, FL USA
[3] Univ Maryland, Condensed Matter Theory Ctr, College Pk, MD 20742 USA
[4] Univ Maryland, Joint Quantum Inst, Dept Phys, College Pk, MD 20742 USA
[5] Univ Geneva, Dept Theoret Phys, CH-1211 Geneva, Switzerland